1. Field of the Invention
The present invention relates to a light source device; more particularly, the present invention relates to a module that employs a plurality of light emitting diodes (LEDs) as a light source, and a display system comprising the light source module.
2. Descriptions of the Related Art
A light emitting construction employing LEDs as a light source is disclosed in U.S. patent application Ser. No. 11/081,825. The light emitting construction emits a light beam with a high driving current in a non-continuous lighting state. This construction forms a basis for a light source module and a projection system comprising the light source module.
A light source module 1 as seen in FIG. 1 comprises a first LED 111, a second LED 112, a mirror wheel 12, and a power control device (not shown). The two LEDs 111, 112, with the mirror wheel 12 being disposed therebetween, are disposed such that their light emitting paths are substantially orthogonal to each other.
The mirror wheel 12 rotating about its axis 123 comprises a plurality of alternately disposed reflective sectors 121 and transparent sectors 122. Through a microscopic breakdown analysis of its operation mode, it can be shown that when the power control device supplies a current to the first LED 111 in order to make it emit light, one transparent sector 122 of the mirror wheel 12 will be synchronously rotated to a position corresponding to a direction in which the first LED 111 emits light, so that the light beam can pass through and exit toward an output direction. Subsequently, when the power control device supplies a current to the second LED 112 instead and switches off the current to the first LED 111, one reflection sector 121 of the mirror wheel 12 will be rotated to a position corresponding to the direction in which the second LED 112 emits light, so that the light beam from the second LED 112 is reflected and propagated toward the same output direction. In this way, the light source as a whole can provide the desired light rays in a fast alternating manner, effectively resulting in continuous light as perceived by the human eye.
FIG. 2 is a schematic graph depicting an alternating emission duty cycle of the aforesaid light emitting structure. More specifically, the alternating emission of the two LEDs will result in an on-state light flux (i.e., the “flat peak section” labeled by symbol A) in the output light source. This setup is adapted to implement a nearly continuous light flux along the time axis as a replacement for the continuous operation mode associated with a single LED, and provides a higher luminance.
However, such an ideal structure still has a defect in practical operation. That is, since reflective sectors 121 and transparent sectors 122 of the mirror wheel 12 are alternately disposed, a number of border regions between the reflective sectors and transparent sectors will be inevitably formed therebetween. In the case that a light beam from either LED impinges entirely or partly on such border regions, not only will a portion of the light beam be lost, but also the instantaneous flux will be degraded.
To avoid the aforesaid light loss, the LEDs must be controlled so that light beam will not be emitted on the border regions. However, since the two LEDs have their positions fixed, the only solution for this setup is to switch off an operating LED in advance when a border region of the mirror wheel 12 is approaching a light beam, after which the opposite LED will be switched on immediately. In other words, the border regions should be accompanied by an off-state (i.e., the “narrow trough section” labeled by symbol B), and only after the border region pass through the LED, can the opposite LED be allowed to emit a light beam.
However, as is well known, a LED is a light source that provides a highly diffusive light beam, rather than an ellipsoidal lamp of collective nature or a parabolic lamp that provides a parallel light beam. As a result, the light beam projected by a LED will actually occupy a substantial area on the mirror wheel 12, and the aforesaid solution of switching on and off for LEDs in advance is impractical to achieve the desired effect. Moreover, using this method to skip the border regions, the numerous borders regions on the mirror wheel 12 will cause a substantial area on the mirror wheel 12 that is unusable at the very onset, which will not only shorten the desirable A sections (“flat peak sections”) and lengthen the undesirable B sections (“narrow trough sections”) in the otherwise continuous light flux, but also exacerbate the discontinuity in the light flux and substantially degrade the efficiency the mirror wheel 12.
In view of this, there exists an urgent need in the art to provide a light source module that partly or completely obviates such disadvantages, and a display system comprising the light source module.